This application claims the priority of Japanese Patent Application No. 2000-040731 filed on Feb. 18, 2000, which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to an illumination optical system for illuminating a liquid crystal display panel or DMD (digital micromirror device), and a projection type display apparatus using this illumination optical system.
2. Description of the Prior Art
Recently, in projection type display apparatus using a light valve such as a liquid crystal, individual constituents have been improved and so forth, whereby those having a higher efficiency and brightness have been developed year after year. For homogenizing the light quantity within the cross section of a luminous flux on the light valve, on the other hand, two integrator plates each comprising a number of lens arrays arranged two-dimensionally are disposed in parallel on the optical axis.
Since it has become possible for projection type display apparatus to illuminate a light valve with bright and uniform light as such, they have come into a wider use. On the other hand, problems have been occurring in that, depending on the place where they are used or their application, images displayed on their screens become too bright to be seen or make viewers fatigue.
Hence, the brightness of illumination light may be adjusted depending on the place of use and the application.
When adjusting the brightness of incident light in a typical optical system, a lens part is provided with a stop, and the amount of opening of this stop is regulated.
Therefore, a projection lens part in a projection type display apparatus may be provided with a stop, which is operated so as to adjust the brightness of illumination light.
If a projection lens is provided with a stop, which is operated so as to adjust the brightness, then the luminous flux whose diameter is to be adjusted by this stop must have been modulated by a light valve beforehand and thus carries image information. As a consequence, errors in the form, position, and operation of the stop greatly affect the image quality. In particular, the stop thermally deforms upon high-temperature heating due to the illumination light, whereby its accompanying deterioration in image quality is not negligible.
Since the temperature of stop member rises as such, it is necessary to provide a cooling structure therefor.
In view of such circumstances, it is an object of the present invention to provide an illumination optical system which can adjust the brightness of illumination light without affecting the image quality and without necessitating a cooling structure in particular, and a projection type display apparatus using the same.
The present invention provides an illumination optical system comprising:
a light source unit;
an integrator unit in which a plurality of integrator plates each comprising a number of lens arrays arranged two-dimensionally are disposed so as to homogenize a luminous flux from the light source unit; and
a light valve for modulating light from the integrator unit according to predetermined image information and outputting thus modulated light;
wherein effective luminous flux quantity adjusting means adapted to adjust a light quantity caused by an effective luminous flux on the light valve is disposed within or near the integrator unit.
In the case where a polarization beam splitter having a comb-shaped polarization separating prism array and a xc2xd wavelength plate is disposed on the light valve side of the integrator unit,
the polarization beam splitter may be made movable in a direction in which the light quantity caused by the effective luminous flux on the light valve is adjustable.
In the case where a polarization beam splitter having a comb-shaped polarization separating prism array and a xc2xd wavelength plate is disposed on the light valve side of the integrator unit,
a light-shielding plate may be disposed between the integrator unit and the polarization beam splitter, and made movable in a direction orthogonal to an optical axis so as to adjust a quantity of light incident on the polarization beam splitter.
A light-shielding plate may be disposed on the light valve side of the integrator unit and made movable in a direction orthogonal to an optical axis so as to adjust a quantity of light emitted from the integrator unit.
Among a plurality of integrator plates constituting the integrator unit, at least one integrator plate may be provided with effective luminous flux quantity adjusting means for adjusting the light quantity caused by the effective luminous flux on the light valve.
Also, the present invention provides an illumination optical system comprising:
a light source unit;
an integrator unit in which a plurality of integrator plates each comprising a number of lens arrays arranged two-dimensionally are disposed so as to homogenize a luminous flux from the light source unit; and
a light valve for modulating light from the integrator unit according to predetermined image information and outputting thus modulated light;
wherein, among a plurality of integrator plates constituting the integrator unit, at least one pair of integrator plates arranged in an optical axis direction have a distance therebetween which is changeable so as to adjust a light quantity caused by an effective luminous flux on the light valve.
Further, the present invention provides a projection type display apparatus comprising one of the above-mentioned illumination optical systems, and a projection lens for projecting onto a screen an optical image carried by light modulated by the light valve.
In the illumination optical system and projection type display apparatus in accordance with the present invention, a structure adapted to adjust the effective luminous flux diameter of illumination light is provided near an integrator unit for homogenizing the light quantity of the luminous flux from a light source.
Since positions near the integrator plate located on the light valve side are set so as to be optically conjugate with the pupil position of a projection lens, regulating a luminous flux near the integrator unit can yield effects on a par with those obtained when the projection lens is provided with a stop so as to regulate the luminous flux.
Even when the luminous flux is adjusted by the integrator unit, the luminous flux is in a state carrying no image information, whereby errors in its adjustment can affect the image quality very little.
Also, since the integrator unit is cooled by a cooling structure inherently disposed in the illumination optical system, it is not necessary to provide separate cooling structures.